Process for making aerosol filters



E. J. HACKNEY ET AL PROCESS FOR MAKING AEROSOL FILTERS Dec. 18, 1956 3 Sheets-Sheet 1.

Original Filed Oct. 7, 1953 INVENTORS EDWARD J. HACKNEY CHARLES D. FAUCETTE BY FREDERICK RDARKIS ATTORNEYS Dec. 18, 1956 E. J. HACKNEY ET AL 2,774,680

PROCESS FOR MAKING AEROSOL FILTERS 3 Sheets-Sheet 2 Original Filed Oct. 7, 1953 IN V EN TORS EDWARD J. HACKNEY ATTORNEYS CHARLES D. FAUCETTE FREDERICK R. DARKIS QOE Dec. 18, 1956 E. J. HACKNEY ET AL 2,774,680

PROCESS FOR MAKING AEROSOL FILTERS Original Filed Oct. 7, 1953 3 Sheets-Sheet 3 m x- N 8 0 o a 0" 2 a; rm g I P INI'ENTORS Z5 EDWARD J, HACKNEY CHARLES D FAUCETTE By FREDERICK RDARKIS WWW ATTORNEYS United States Patent 2,774,680 PROCESS FOR MAKING AEROSOL FILTERS Edward J. Hackney, Charles D. Faucette, and Frederick R, Darkis, Durham, N. C.

Original application October 7, 1953, Serial No. 384,684. a

This invention relates to aerosol filters, and to a process and machine for making them. While the filter is believed to be useful for the filtration of any kind of aerosol or particulate suspension or dispersion in a gaseous medium, such as smoke, fog and the like, the following description sets forth by way of example a filter according to this invention which is especially adapted to be a used in and to form part of a cigarette where the aerosol dispersion to be filtered is smoke produced by the burning of tobacco in the cigarette, being drawn into the mouth of the smoker.

Among the objects of the invention are to provide an aerosol filter which provides a large number of small fibers lying at right angles to the direction of gas movement through the filter, which permits such fibers tobe preselected in accordance with the characteristics of the aerosol to be filtered, which permits the pressure drop through the filter to be predetermined, and which is especially effective in absorbing nicotine from tobacco smoke.

Other objects of the invention are to provide a process of making an aerosol filter in which spun textile filamentary material, which is to constitute the matrix of the filter, may be efliciently and conveniently provided with a fuzz-like attachment consisting of short rod-like particles or fibers of microscopic size, in which a tow of filaments of spun textile material is opened up and spread apart by electrostatic repulsion in order to prepare such filaments for further-treatment, in which filaments of such material are passed through'an agitated cloud of rod-like particles of microscopic size, while the filaments themselvesare charged, in order to cause the rod-like particles to orient themselves as they enter the field of the chargedfilaments'an'd to become attached thereto in a generally'oriented relationship thus forming the fuzz.

Other objects "of the invention are to-provide machi'nery or apparatus for making an aerosol filter in which powered rollers having a'surface of hard'high-dielectric material are adapted'to draw a tow of spun textile filaments through a pairofbraked rollers havingsimilar surfaces, whereby electrostatic charge is generated in' the filaments of the tow and the tow is thereby opened up and spread apart by the mutual repulsion ofthe. filaments,

thus preparing it for further treatment; and ,ir'r which electrostatically' charged filaments of spun" textile ma-Q terial are passedthrou'gh an applicator chamber i'r'i which feeder rollers and beater fans-maintain in proximity to the moving filaments an agitated cloud or'suspension of rod-like particles of microscopic size whichadhere' to the surface of the filaments in oriented manner to form a fuzz-like attachmentthereto.

,This application is a division of our applicationi'Serial No. 384,684, entitled Aerosol Filters and a Process and Machine for Making Themf Our applications Serial No. 444,883 filed July 6, 1954.) and entitled .iM'iachine for Making Aerosol Filters, andSerial No. 444,884

Patented Dec, 18, 1956 p 2 filed July 6, 1954, and entitled Aerosol Filter Making Machine, are related applications also divided from the said parent application Serial No. 384,684.

In the drawings annexed to and. forming part hereof Fig. 1 shows a filter tipped'cigarette; I ,jFig. 2 is a longitudinal section through the .ffilter and adjacent portions of a filter-tipped cigarette;

Fig. 3 is a section in the plane 3'3 of Fig. 2; I Fig. 4 is a perspective of a portion of a cigarette filter 18 according tothis invention, somewhat diagrammatic inform;. 7 n

Fig. 5' is, a section through one of theffilarrients '19, showing attached thereto a few of the oriented rod-like fibers '20, asseen-under amicr'oscope;

Fig. 6' is a diagrammatic longitudinal sectionthrough a machine according to this invention for making aerosol filtersfwith some parts in section and other parts in elevation;

Fig. 7 is a vertical section in the planes 7-7 of Fig.

6, showing a portion of the fiber-applicator box 55; v Fig. 8 is a horizontal diagrammatic section, looking downwardly, in the planes 88 of Fig. 6, showing the apparatus which stretches and charges the filament, and spreads the tow, thus readying it for further treatment;

Fig. 9 is a vertical section in the plane 9-9 of Fig. 6, showing the air blast which completes the spreading of the filaments in. the tow;

Fig. 10 is a diagrammatic drawing to.,il1ustrate what is believed to bethe mechanism by which the rod=like fibers 20 become oriented as they enter the field of the charged filament19 in the fiber-applicator box 55; and

Fig. 11 is a section in the planes 111 1 of Fig. 6, showing the, means by which the spread tow-, after treatment, is gatheredinto' acompact bundle.

The 'following, which describes the making of filters for filter-tipped cigarettes,- is set forthforpurposes of illustrationand not to" limit the invention,- as hereinafter claimed. i a

f The filter structure A filter according to this invention; comprises two main elementsgwhichmayand usuallywill for convenience be made of diiferen't'materials, thoughthey can be of the same material if desired. 'The first is the supporting matrix composed of long filaments, in most cases as long as the 7 gas path through the filter and disposed generally in a direction parallel to t e direction of gas movement.- These filaments are not necessarily or usually straight (aswire rod-like fibersjeixtends generally at rightangles to the direction of gas flow through the filter. Normally a very large :number of: such rod-like fibers areattached to the surfaces of the filaments, forming a sortof thereon. The filter as a whole, consists of a compact package or bundle oi-jmatrix filaments extending generallyparallel to each otherand' to the direction of gasmovementj through the filter, lthe'su'rfaces of these filaments bearing the fuzz above-mentioned, and the entire bundle being enclosed with a wrapper'impervious to gas at theprevailing pressure, which surrounds the sidesof the bundle and leaves the endsfopenfor theentrance and exit of gas. By suitably selecting the .diameter 'and kinkiness of the matrix filaments the character and density of the fuzz deposited along their peripheral surfaces, and the degree of compactness of the bundle when made up into a finished filter structure, this invention enables a filter to be made in which pressure drop is reproducible and controllable; and Which may be manufactured to have predetermined characteristics for the removal of aerosolparticles of differing size distributions and densities according to the nature of the smoke, fog or the like to be filtered.

In general, the matrix filaments may be of any kind of spun textile material. Examples are the synthetics such as rayons, proteins, nylons, vinyls, fiber glassand their analogues. Carded or combed naturally-occurring fibers may also be used in some forms of filters. In general the material of the matrix filament should be one which is not deleteriously affected by contact with the gaseous medium to be filtered, and which does not deleteriously afiect, as by desorption or otherwise, the gaseous medium which issues from the filter.. A special requirement in the case of cigarette filters is that the filament be non-toxic and assimilable if taken into the mouth.

Filamentary diameter and kinkiness are important chiefly for the bearing they have upon pressure drop. Pressure drop depends, for any given type of material used in accordance with this invention, upon the degree of lateral compression to which the bundle of matrix filaments is subjected when it has been assembled into a filter body, the frequency and degree of kinking and diameter of the matrix filaments, the density, diameter and length of the applied fuzz, the type of gaseous medium to be filtered, the length of the filter and the ratio of crosssectional area of matrix'filaments to the total cross-sectional area of the filter. These factors may be varied at will in using the invention and it is one of the advantages of the invention that when a filter of desired pressure drop and extractive power has been made according to the invention other filters can be made reproducing the desired performance by keeping the named factors the same.

For example, cellulose acetate of high acetone solubility, spun .into continuous filaments about 35 to 55 microns in diameter and having, prior to stretching, about 9 crimps per inch, forms a satisfactory matrix filament for use in a cigarette filter. If the filter plug in such a cigarette is to be a half inch long, and to have a fuzz as hereinafter described, satisfactory pressure drop for comfortable smoking is achieved when about 5000 such filaments are compacted into a filter about /1 in diameter, which is average cigarette size. Under these circumstances the total cross-sectional area of the matrix filaments occupies about 14% of the total cross-sectional area of the filter.

The'rod-like fibers which, according to this invention, are adherent to the peripheral surfaces of the matrix filaments and are oriented so as to extend in a direction generally at right angles to the direction of gas flow through the filter, may consist of any fiber-like material Whose particles are of substantially greater length in one axis than in an axis at right angles thereto and preferably are rod-like in form. For convenience in exposition, and by Way of illustration, these particles will be described herein as if they were short sections of solid rod, circular in cross-section, and of length substantially greater than their diameter. They are herein called fibers.

For high efiiciency in filtering an aerosol-containing gas, it is necessary to provide in the filter a very large number of rod-like fibers disposed at right angles to the axis of gas fiow. The rate at which such fibers capture aerosol particles suspended in the moving gas stream depends, among other things, on the diameter of the fiber and the diameter of the particles. In general, relatively large fibers have a low capture-rate for the very small particles. In cigarette smoke as it reaches a cigarette filter the particles range in size from about 0.1 to 15 microns in diameter. In order to provide a satisfactory rate of capture for particles near the smaller end of this range, it is necessary that the diameter of the fibers be less than about 25 microns. While this is a relative matter, and fibers of larger diameters may be used when less eificient filtration of smaller particles can be tolerated, we have found that fibers of diameter from about 5 to 25 microns are satisfactory for cigarette smoke, although with fibers of this size capture-rate appears to fall off in respect to particles smaller in diameter than about 0.3 micron. For most aerosol suspensions it may be said that the diameter of the fibers should not exceed about 40 microns or the diameter of the matrix filaments whichever is less.

The length of the fibers, on the other hand, may be materially greater than their diameter. Where it is.desired to compact the matrix filaments very closely together, so that the gas spaces between them are restricted, the desirable length of the rod-like fibers may be very short, on the order, say, of -15 tov 50- microns. Where, however, more space is available between the matrix filaments, Whether because of their crimping or because they are to be spaced farther apart to avoid excessive pressure drop, fibers may be employed having a greater length. For example, in making cigarette filters a convenient and desirable fiber-length is about 300 microns. In general, the upper limit of length for these fibers is that at which they no longer exhibit the function of orientation when they enter the electrostatic field of the filament, as hereinafter disclosed. The rod-like fibers may consist of any natural or synthetic substance which is not deleteriously affected by the gaseous medium to be filtered, and does not deleteriously affect, by desorption or otherwise, the gaseous medium issuing from the filter. Other specific requirements may exist in particular cases. For example, in the case of a filter to be used in a cigarette, this substance should be one which is non-toxic and assimilable if taken into the mouth.

In the filter of a filter-tipped cigarette there is used, according to this invention, particles of alpha cellulose, the preferred form and size being rod-like fibers having an average diameter of about 15 microns and a length of about 300 microns, with examples of measured diameter from 8 to 24 microns, and of measured length from 70 to 620 microns.

The means to enclose the sides of the bundle of filaments, and thus to. complete the filter, may be any material which is substantially impervious to gas at the pressures which prevail when the filter is in use. A steel container is one'example. In the case of a cigarette filter, the enclosing means is preferably a paper tube with overlapped margins adhesively secured together. In any case the ends of the matrix filaments are left free or else in communication with a suitable gas passageways.

A filter-tipped cigarette embodying this invention is shown in Figs. 1 to 4. The cigarette 15 comprises a paper wrapper 16 containing tobacco 17 and a filter plug indicated generally at 18. The filter plug includes a bundle of cellulose acetate filaments 19, each filament having a multiplicity of rod-like fibers 20 adherent to its peripheral surface, the entire bundle of filaments being enclosed within a paper wrapper 21. Filaments 19 and paper wrapper 21 are of equal length, preferably about a half inch. Cigarette wrapper 16 fits snugly about plug wrapper 21. The two may be secured together by adhesive if desired. Preferably a mouth-piece wrapper 22 of waterproof paper may be wrapped around'that end of the cigarette which contains plug 18.

The above-described filter may be manufactured by first causing a tow of raw matrix filaments, as drawn from supply, to become electrostatically charged; then passing the tow, through an agitated suspension in air of the fibers which are to be adhered to the surface of the filaments; and finally assembling the filaments into 'a bundle which is then suitably enclosed as by a paper tube. The result of agitating the suspension of fibers inlair, usually done by mechanical means such as a fan, is to cause the fibers to acquire electrostatic charges by air friction, and these charges it is believed play a part in the subsequent orientation of the fibers when they enter the electrostatic field surrounding each charged filament. The electrostatic field 23 (see Fig. 10) surrounding each filament 19 as it travels through the cloud of fibers, causes each individual fiber within that field, for example, fiber 24, to be rotated about its center and drawn towards filament 19, to which it strongly adheres (see Fig. 5). Thereafter the filaments, having thus acquired a sort of fuzz, are assembled together in a bundle and provided with an enclosure which maintains them in assembled and generally parallel relation. Such a bundle is illustrated by filter plug 18 shown in Figs. 2 and 3.

In order to explain more fully how this process may be carried out, there is disclosed herein one form of apparatus (which in itself forms part of this invention) suitable for carrying out the process of the invention. The apparatus disclosed is primarily intended for the manufacture of filter plugs to be incorporated into cigarettes, but with obvious modifications can be used for the manufacture of filters embodying the invention that are made for other uses.

Apparatus for making the filter Referring to Figs. 6, 7, 8, 9, and 11:

From a supply reel 25 a tow 26 is drawn consisting of the number of spun textile filaments desired in the completed filter. Rollers 27 and 23 are mounted upon respective bearings 29 and 30, the bearing 29 being movable towards and from the bearing 3%. Suitable means, for example screw-threaded clamps 31 and 32, enable the cylindrical faces of rollers 27 and 28 to be moved towards each other and held under compression at their line of contact or bite 33.

Two powered rollers 34 and 35 are mounted upon respective bearings 92 and 93, the bearing 92 being movable towards and from bearing 93 under control of screw-threaded clamps 94 and 95 so that 'therollers may be held under predetermined compression at their line of contact or bite 36. Rollers 34 and 35 are driven from .a variablespeed gear box 37 controlled by lever 37a. The arnangementis such that tow 26, drawn from supply 25, passes between the bite 33 of rollers 27, 28, then around and in contact with a portion of the peripheral surfaces of each of rollers 28 and 34, and then passes between the bite 36 of powered rollers 34, 35. Each of rollers 27, 28, 34 and 35 is covered on its peripheral surface with a tread 38 of hard high-dielectric material, for example, hard rubber. When the clamps 31,32 are tightened to press rollers 27 and 28 into engagement with each other, the effect in ooaction with their bearings is that these rollers become braked, and the portion of the tow at 91 passing from the braked rollers 27, 28 to the powered rollers 34, 35 ishighly stretched. In order that the stretching action may give rise to high friction between the tow and the surfaces of braked roller 28 and powered roller 34, the tow'is arranged in its passage through the rollers so that it first passes around and in contact with a portion'of the rubberized periphery of one of the braked rollers after leaving the bite'between them, and then passes around and in contact with a portion of the rubberized periphery of one of the powered rollers before entering the bite between them. Thus the stretching action of the tow at 91 between bite 33 and bite 36 is accompanied'by slippage of the tow under heavy tension against the hard rubber surfaces of rollers 23' and 34. By reasonof this slippage under heavy tension, each of the .several filaments in the tow acquires a substantial electrostatic charge from one or the other or both of said rubberized surfaces.

Since the several filaments in the tow have, by reason of the above stretching and sliding action received like charges, they become mutually repulsive and as the tow I 6 41 beneath an air'blast device 40 fed with air from a pump 42 and having side guide walls 96 and 97. The tow leaving the air blast device at 45 is at its maximum separation. For example, a tow comprising about 5000 filaments of 16 denier and intended to form the filter plug for a cigarette, will at 45 be in the form of a flattened ribbon from 4 /2 to 6 inches in width and of a thickness preferably not greatly exceeding the thickness of one or two filaments. At this point, and until the tow is finally condensed in funnel 83, the individual filaments are generally at such distance from each other as to show visual separation at least of the major groups, but most filaments remain within the electrostatic field of their neighboring filaments whereby the tow is kept in its spread condition. 9

Powered roller 46 receives the flattened tow coming from the air blast device, and directs it in an upward direction into an adhesive applicator box 47 through which the tow passes while in flattened condition. The application of adhesive is not necessary to the realization of the advantages of this invention, but is desirable in the manufacture of filters which are intended for use in cigarettes. The reason is that the adhesive, when hardened, promotes cross-linking between matrix filaments and thus gives to the filter body the added degree of strength which seems to be necessary to enable the finished filter plug to withstand the action of cutting knives without distortion.

Adhesive may conveniently be applied in applicator box 47 through spray nozzles 48, 49 fed by pump 50 from a source 51 and atomized by air supplied by pump 98. Since the openings 52 and 53 through which the flattened'tow enters and leaves applicator box 47 would permit escape of adhesive spray, means is provided to maintain a negative pressure within box 47. This may conveniently take the form of a pump 54 adapted to draw adhesive spray or mist from the interior of box 47 and to return it to source 51, through a separator (not shown) if desired.

From adhesive applicator box 47 the flattened ribbon of tow passes to the fiber applicator box 55 having openings 56 and 57 through which the tow enters and leaves the box. Applicator box 55 consists of a hopper portion 58 and an agitation chamber 59. A door 60 permits finely-divided fiber material to be introduced into-hopper 58.

Positioned in the lower part of hopper 58 are a pair of powered fluted feed rollers 61, 62, positioned respectively adjacent the inwardly .sloping side walls 63, 64 of hopper 58. Between rollers 61 and 62 are mounted a pair of walls 99, 100 forming a channel 65 through which the tow is adapted to pass. Each of walls 99 and is provided at its lower end with a curved shoe 102, 103, concentric respectively with the cylindrical surface of revolution'described by the outer edges of the flutes of the rollers 61 and 62 and closely adjacent thereto. Thus each fluted roller and its shoe forms a feeder of predei for example 1800 R. P. M., by motors 67a and68a releaves the bite 36 it exhibits a marked tendency to spread laterally (see Fig. 8, at place marked 39). v

In order to assist the separating or spreading tendency .of the tow, it may then if desired be run overa table termined size for delivering fiber particles from hopper 58 to agitation chamber 59.

In the agitation chamber 59 of box 55 are suitably journaled and positioned a pair, and preferably two pairs, of agitator fans 67, 68 powered to rotate at high speed,

spectively. Such fans may be made as follows: Upon a shaft 69 'are secured two flat circular. plates-7i) and 71 (see Fig. 7 Upon the flat surface of each plate are secured a series of curved blades 72 projecting at right angles to the plane of the plate and adapted to rotate with it. The fans are powered to rotate in such direction that the blades, in their nearest approach to the path of the tow, move in an upward direction (see Fig. 6). Thus Y fiber'particles are propelled in a direction parallel to the direction of movement of the tow, (and towards the same, and the suspension of these particles in the air isrnaintained in the form of a dense' and agitated cloud through which the charged filaments pass andin which they attract large numbers of fiber particles.

To aid rollers 61, 62 in feeding finely-divided material to agitation chamber 59, it is desirable to secure a pair of powered vibrators 101, 102 (see Fig. 7) to the outer walls of hopper 58. To prevent the escape of fiber particles through openings 56 and 57, a pump 73 is arranged to draw air from box 55 and to discharge it into a separator 76 containing a cloth bag 74, an air escape vent 75 and a removable cover 77. Finely-divided material recovered in bag 74 may be returned to the system through door 60.

After passing over rollers 80 and 81 and leaving box 55 through opening 57 the tow at 78 is in the form of a flattened ribbon consisting of a plurality of filaments each having on its surface a layer 79 of adhesive material and also having adherent thereto a large number of particles of finely-divided fibers (see Fig. This tow after passing around the powered roller 82 enters condensing funnel 83. At point 84 (see Fig. 11) the tow is about to be gathered into a bundle of desired external configuration. At point 85, where it emerges from funnel 83, the tow has been gathered into a bundle possessing the desired cross-sectional configuration which, in the case of filters made to be incorporated in cigarettes, is substantially circular in outline and about 7 in diameter. It is then ready to be enclosed in a suitable wrapper.

In the case of filters made to be incorporated in cigarettes, the wrapper is a paper tube. Preferably the bundle formed in funnel 83 is advanced into a forming tube 36 (see Fig. 6) where it is continuously wrapped in a strip of paper 87 drawn from a source 88. The machine for wrapping the bundle of filaments 85 in a tube of paper 87, and cutting the same off into tubes of desired length by means of knife 89, is essentially the same as the known machinery for the manufacture of cigarettes. Such machines are well known and will not be described in detail here.

In manufacturing filter-tipped cigarettes as shown in Figs. l-4, it is preferable to form an intermediate product 90 consisting of a continuous bundle of cellulose acetate filaments, with adherent finely-divided fibers, which is about 3 inches long and is contained in a paper tube of the same length. Such intermediate product is afterwards severed into appropriate half-inch lengths for insertion in individual cigarettes. This may be done automatically in known machines which need not be here described.

If the nature of the adhesive requires the subsequent application of heat in order to set or bake it, intermediate product 90, handled in the same manner as cigarettes, may be introduced into low-temperature baking ovens for the required length of time.

Process of making the filter The process of manufacture according to this invention may now be more fully described, having reference to the aforementioned apparatus, by way of example only. For illustration the process to be set forth pertains to the manufacture of cigarette filters.

Applying the electrostatic charge.-Preferably the electrostatic charge is applied to a tow of spun textile filaments such as cellulose acetate by friction with a hard, high-dielectric solid. If desired, however, the charge may be applied in other known ways, asfor example by riction with gas molecules such as a hot-air blast, by corona discharge, or by administration of a direct electrical charge. In the preferred form of the process the tow is drawn from a source of supply through the bite of a pair of braked rollers having hard rubber surfaces by means of a pair of powered rollers having similar surfaces. The tow may be threaded through the rollers in such manner that it passes around a portion of one of the braked rollers after leaving the bite between them, and around a portion of one of the hesive to a prompt completion.

powered rollers before entering the bite between them. Thus a pronounced stretch is introduced into the filaments of the tow, by reason of the resistance of the braked rollers, and the individual filaments of the tow are brought into hard slipping engagement with the surface of the rollers, thus acquiring a strong electrostatic charge. The existence of this charge is made evident by the tendency of the tow to spread as it leaves the powered rollers, the individual filaments at this point being similarly charged and mutually repulsive.

Further spreading the row by air blast.If desired or necessary, the individual filaments of the tow may be further separated and spread apart by suitable air blast applied thereto after the tow leaves the powered rollers above-mentioned. Such a device is indicated at 40.

When the tow has been flattened into a ribbon of substantial width and a thickness preferably not much more than that of one or two filaments, and each filament bears a strong electrostatic charge, it is then ready for application of finely-divided fibers. Such application may take place immediately, or may be preceded if desired by application to the tow filaments of a layer of adhesive material. At this time and during the subsequent stages of treatment, each or most of the individual charged filaments continue to be within the electrostatic field of at least its neighboring filaments, and thus under the influence of a force tending to keep the filaments separated one from another.

Applying the adhesive.The application of adhesive to the filaments is by no means necessary to secure firm adherence of the fibers thereto. Electrostatic attraction is sufficient to assure a permanent attachment between the fibers and the peripheral surfaces of the supporting filaments, and such attraction will last indefinitely even after the filter has been incorporated in a cigarette. (See Filter No. 3 below.) The use of an adhesive is, however, desirable in the manufacture of filters for use in cigarettes, in order to give the filter plug as a whole the necessary degree of rigidity and resistance to compression which will permit it to be cut without deformation by the knives of a cigarette-making machine. For this purpose it is preferred to coat the peripheral surfaces of the filaments before they pass to the fiber applicator box, with a layer of a substance which is a solvent for the particular filament used. Then, when the surface of the filament has been Wetted with such solvent and a soft solid solution has formed, contacting filaments Will tend to stick together and thus give the entire filter bundle greater internal strength. It is usually desirable to heat the filter plugs, after the manufacture of the intermediate product is completed, in order to harden or dry the surface of the filament, particularly if the same is to be used immediately in cigarette manufacture.

It is also desirable, when making a cigarette filter, to use an'adhesive which will not give any noticeable taste to the smoke issuing from the filter into the mouth of the smoker. In making cigarette filters in which the filaments are made of cellulose acetate, the preferred adhesive is triethyl citrate. After the intermediate products 90 have been made, they may be heated for about two hours at F. in order to bring the setting of the ad- However, the hardening of the adhesive occurs spontaneously at a slow rate and ultimately the desired degree of firmness can be achieved without'heating, if a sufiicient length of time is available.

Applying the fibers.Whether or not the filaments have been coated with adhesive, the next step of the process is to move the ribbon-like flattened band of charged filaments into a zone where they pass in intimate contact with an agitated suspension or cloud of finelydivided fibers which, as above stated, may be of any material of appropriate size and non-deleterious material, but preferably consist of small rod-like particles of alpha cellulose having a diameter from about 8 to 24 microns (average 15) and a length offrom about 70 'to 620 microns (average 300). Each fibrous particle of microscopically small size, such as the alpha cellulose just described, has the property when it has entered the field surrounding a charged filament, of rotating in space till its end oppositely charged from that of the filament is nearest to the filament, and as thus oriented it is drawn towards the surface of the filament until it makes contact therewith. This end of the fiber isthen strongly held in contact with the filamentary surface while the opposite end of the fiber is repelled thereby. The result is that, in general, the fibers which become attached to the peripheral surfaces of thecharge'd filaments stand out therefrom in a manner which might be characterized as resembling a fuzz, although under a microscopethe fuzz does not appear particularly dense.

The quantity of fibers picked up by the filaments can be controlled by regulating the speed at which the filaments pass through the cloud and the density of the cloud. The greater the speed, or the less the density, or both, the less will be the pick-up of fuzz.

Assembling and wrapping the bundle.Afte'r the tow of spread and charged filamentshas been passed through an agitated cloud of fiber particles, as described, the tow is then passed to a funnel or the like where it is gathered into a compact bundle preferably of circular outline as seen in cross-section, and thence fed directly to a place where it is automatically and continuously wrapped in a paper tube. Examples Five cigarettes, each containing afilter plug, were made and tested for weight of material removed by the filter per puff of smoke. The plugs were made from cellulose acetate tow in which the individual filaments were 16 denier and the total denier of the tow was 117,000 before stretching. The individual filaments contained on the average 9 crimps per inch before stretching. During No. 1 where no fibers Were;used)' consisted ofalpha cellulose in the form of rod-like particles which, by measurement, were found to be from 8v to- 24 micronsindiameter (average 15 microns) and from 70to 620 microns in length (average 300 microns).

The adhesive material was triethyl citrate. In each case about 5,000 cellulose filaments, comprising an aggregate cross-sectional area calculated to be 0.01135 sq. in., was formed into a bundle one half inch long and wrapped in a paper tube toform a plug having a total cross-sectional area of 0.0822 sq. in. Thus the aggregate cross-sectional area of the filaments, by calculationpwas 13.8% of the total cross-sectional area of the plug. This however does'not take into account cross-linking between filaments caused by the adhesive nor the area occupied by the alpha cellulose fibers. p v FILTRATION EFFECTIVENESS or rrv'n CIGARETTE FILTERS MADE AS ABOVE-DESCRIBED AND DIFFERING FROM EACH OTHER AS SHOWN IN THIS'TABLE As a percent of Total Weightin i 1 the Filter Milligrams of Smoke Filter No. Removed Cellulose Alpha per Puff 1 Acetate Adhesive Cellulose Filaments Particles 1 PufP' means the passage or31 cc.- of-air.into a lighted cigarette for a period of 2 seconds, repeated once every minute.

The foregoing shows that a bundle of cellulose acetate filaments free of adherent alpha cellulose fibers possesses some ability to capture aerosol particles from a gas passing through the filter, but that such ability is limited. It is believed that, if the cellulose acetate filaments were perfectly straight like rodsof glass or metal, capture of aerosol particles would be limited to larger particles which have an appreciable Stokes law rate-of-fall, and would not include particles less than 0.3 micron in radius. At the same time the above figures indicate that the presence of alpha cellulose particles, attachedto the peripheral surfaces of the cellulose acetate filaments in the manner herein disclosed, substantialy increases the total weight of material removed from the gas stream. The effectiveness of the filter in removing such'material increases with increase in the quantity of alpha cellulose particles present, until the number thereof "causes too great a pressure drop for comfortable smoking While the above invention has been described primarily with reference to filters and their manufacture for incorporation in and as part of a cigarette, which said filters are of relatively small diameter and short gas path, it is intended that this invention shall include filters and their manufacture for other applications such as for use in gas masks, air purification systems, ventilation, industrial smoke and dust control, dehydration of vapors, and the like. This invention is npt limited to the specific means or steps or apparatus herein shown and described but extends to and includes all equivalents thereof which, in the combinations recited in the subjoined claims, operate in the same or similar manner to achieve the results therein set forth. V i

While the spun textile filaments are here described for illustration as being disposed generally parallel to lationship thereto.

,the direction of gas' fiow through the filter, and no twisting is produced in condensing funnel 83 as here shown, a filter may be made in accordance with this invention in which the filaments, after the fuzz has been applied and the tow gathered into round form, are then twisted. together so that they occupy helical paths in the filter. Such twisting will, of course, cause the path of gas-flow to be correspondingly twisted, but the filaments will nevertheless continue to be generally parallel to the di- 'rection of gas-flow. Such twisting may be employed to assist in keeping the bundle compact, or as a further control in'assuring a desired degree of pressure drop.

While the'rod-like fibers are herein described for illustration as being at right angles, or generally at right angles,'to the'direct'ion of gas flow through the filter or to the axis of the filter plug, in practice such fibers may be disposed in a somewhat heterogeneous angular re- It is believed that the most efficient use of the'fibers is made when a majority of them are substantially at right angles, as stated, but thisis not essential to the invention since the only efiect of. having a majority of the fibers at an angle other than a right angle is to make a less eflicient use of the available material. The effective length of a fiber for filtering purposes is, of course, a projection-of the fiber in a plane at rightangles to the direction of gas flow.

In the apparatus herein shown theseveral moving parts may all be powered from a common source, which may be the motor which drivestbe forming and cutting mechanism 86, 89. Power from this motor may be communicated (by means not shown) to ashaft 103. 1 From shaft configuration, as shown in Figs. 6 and 11. This shape appears to produce a more satisfactory distribution of alpha cellulose fuzz throughout the cross-sectional area of the filter.

What is claimed is:

1. The process of making an aerosol filter which includes moving a flat band consisting of generally parallel filaments of textile material, all of said filaments bearing a similar electrical charge tending to separate the filaments and a majority thereof being within the field of at least a neighboring filament, into and through an atmospheric suspension of rod-like fibers of diameter not exceeding about 40 microns or the diameter of the filaments whichever is less, and gathering said filaments into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation .to said filaments and with said fibers extending across said passage spaces in spaced relation along said spaces.

2. The process of making an aerosol filter which includes moving a flat band consisting of generally parallel filaments of textile material, all of said filaments hearing a similar electrical charge tending to separate the filaments and a majority thereof being within the field of at least a neighboring filament, into and through an atmospheric suspension of particles of alpha cellulose not exceeding along their minor axes the diameter of the filaments, and gathering said filaments into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said particles extending across said passage spaces in spaced relation along said spaces.

3. The process of making an aerosol filter which includes moving a fiat band consisting of generally parallel filaments of cellulose acetate, all of said filaments bearing a similar electrical charge tending to separate the filaments and a majority thereof being within the field of at least a neighboring filament, into and through an atmospheric suspension of rod-like fibers of diameter not excee'ding about 40 microns or the diameter of the filament whichever is less, and of length not exceeding about 1000 microns, and gathering said filaments into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said fibers extending across said passage spaces in spaced relation along said spaces.

4-. The process of making an aerosol filter which includes moving a fiat band consisting of generally parallel filaments of cellulose acetate, all of said filaments bearing a similar electrical charge tending to separate the filaments and a majority thereof being within the field of at least a neighboring filament, into and through an atmospheric suspension of particles of alpha cellulose of sizes not exceeding about 1000 microns along their major axes and the diameter of the filaments along their minor axes, and gathering said filaments into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said particles extending across said passage spaces in spaced relation along said spaces.

5. The process of making an aerosol filter which includes moving a flat band consisting of generally parallel filaments of cellulose acetate having a diameter of about 35 to 55 microns, all of said filaments bearing a similar electrical charge tending to separate the filaments and a majority thereof being within the field of at least a neighboring filament, into and through an atmospheric suspension of rod-like fibers of diameter not exceeding about the diameter of the filaments and of length not exceeding about 1000 microns, and gathering said filaments into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said fibers extending across said passage spaces in spaced relation along said spaces.

6. The process of making an aerosol filter which includes moving a flat band consisting of generally parallel filaments of textile material having a diameter of about 35 .to 55 microns, all of said filaments bearing a similar electrical charge tending to separate the filaments and a majority thereof being within the field of at least a neighboring filament, into and through an atmospheric suspension of particles of alpha cellulose of sizes about 8 to 24 microns along their minor axes and to 620 microns along their major axes, and gathering said filaments into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said particles extending across said passage spaces in paced relation along said spaces.

7. The process of making an aerosol filter which includes moving a fiat band consisting of generally parallel filaments of cellulose acetate having a diameter of about 35 to 55 microns, all of said filaments bearing a similar electrical charge tending to separate the filaments and a majority thereof being within the field of at least a neighboring filament, into and through an atmospheric suspension of particles of alpha cellulose of sizes about 8 to 24 microns along their minor axes and 70 to 620 microns along their major axes, and gathering said filaments into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said particles extending across said passage spaces in spaced relation along said spaces.

8. The process of making an aerosol filter which includes moving a plurality of filaments of textile material each bearing a similar electrical charge tending to separate the filaments into and through a treatment zone, propelling against said filaments in said zone an atmospheric suspension of rod-like fibers of diameter not exceeding about 40 microns or the diameter of the filaments whichever is less, and gathering said filaments after their passage through said zone into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said fibers extending across said passage spaces in spaced relation along said spaces.

9. The process of making an aerosol filter which includes moving a plurality of filaments of textile material each bearing a similar electrical charge tending to separate the filaments into and through a treatment zone, propelling against said filaments in said zone to an atmospheric suspension of particles of alpha cellulose not exceeding along their minor axes the diameter of the filaments, and gathering said filaments after their passage through said zone into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said particles extending across said passage spaces in spaced relation along said spaces.

10. The process of making an aerosol filter which includes moving a plurality of filaments of cellulose acetate each bearing a similar electrical charge tending to separate the filaments into and through a treatment zone, propelling against said filaments in said zone an atmospheric suspension of rod-like fibers of diameter not exceeding about 40 microns or the diameter of the filaments whichever is less, and gathering said filaments after their passage through said zone into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said fibers extending across said passage spaces in spaced relation along said spaces.

11. The process of making an aerosol filter which includes moving a plurality of filaments of textile material each bearing a similar electrical charge tending to separate the filaments into and through a treatment zone, propelling against said filaments in saidzone an atmospheric suspension of particles of alpha cellulose of sizes not exceeding about 1000 microns along their major axes and the diameter of the filaments along their minor axes, and gathering said filaments after their passage through said zone into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to 13 said filaments and with said particles extending across said passage spaces in spaced relation along said spaces.

12. The process of making an aerosol filter which includes moving a plurality of filaments of cellulose acetate having a diameter of about 35 to 55 microns each bearing a similar electrical charge tending to separate the filaments into and through a treatment zone, propelling against said filaments in said zone an atmospheric suspension of rodlike fibers of diameter not exceeding about the diameter of the filaments and of length not exceeding about 1000 microns, and gathering said filaments after their passage through said zone into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said fibers extending across said passage spaces in spaced relation along said spaces.

13. The process of making an aerosol filter which includes moving a plurality of filaments of textile material having a diameter of about 35 to 55 microns each bearing a similar electrical charge tending to separate the filaments into and through a treatment zone, propelling against said filaments in said zone an atmospheric suspension of particles of alpha cellulose of sizes about 8 to 24 microns along their minor axes and 70 to 620 microns along their major axes, and gathering said filaments after their passage through said zone into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said par- 14 ticles extending across said passage spaces in spaced relation along said spaces.

14. The process of making an aerosol filter which includes moving a plurality of filaments of cellulose acetate having a diameter of about to microns each bearing a similar electrical charge tending to separate the filaments into and through a treatment zone, propelling against said filaments in said zone an atmospheric suspension of particles of alpha cellulose of sizes about 8 to 24 microns along their minor axes and to 620 microns along their major axes, and gathering said filaments after their passage through said zone into a compact bundle in contiguous relation with gas flow passage spaces therebetween in longitudinal relation to said filaments and with said particles extending across said passage spaces in spaced relation along said spaces.

References Cited in the file of this patent UNITED STATES PATENTS 2,034,008 Taylor Mar. 17, 1936 2,047,525 Thode July 14, 1936 2,053,123 Alles Sept. 1, 1936 2,372,437 Lathrop et al. Mar. 27, 1945 2,614,655 Katz Oct. 21, 1952 FOREIGN PATENTS 655,278 Great Britain Jan. 23, 1952 

1. THE PROCESS OF MAKING AN AEROSOL FILTER WHICH INCLUDES MOVING A FLAT BAND CONSISTING OF GENERALLY PARALLEL FILAMENTS OF TEXTILE MATERIAL, ALL OF SAID FILAMENTS BEARING A SIMILAR ELECTRICAL CHARGE TENDING TO SEPARATE THE FILAMENTS AND A MAJORITY THEREOF BEING WITHIN THE FIELD OF AT LEAST A NEIGHBORING FILAMENT, INTO AND THROUGH AN ATMOSPHERIC SUSPENSION OF ROD-LIKE FIBERS OF DIAMETER NOT EXCEEDING ABOUT 40 MICRONS OR THE DIAMETER OF THE FILA- 